1. Field of the Invention
The present invention relates to a layered double hydroxide membrane and a layered-double-hydroxide-containing composite material.
2. Description of the Related Art
Layered double hydroxides (hereinafter also referred to as LDHs), such as hydrotalcite, are compounds that contain exchangeable anions between hydroxide layers. To make use of their characteristics, LDHs have been used as catalysts and absorbents, as well as dispersants in polymers in order to improve heat resistance of the polymers. In particular, LDHs have recently been attracting attention as materials that exhibits hydroxide ion conductivity, and studied for use as electrolytes in alkaline fuel cells or additives in catalytic layers of zinc-air batteries.
Their traditional uses, such as catalysts, require high specific surface area, and thus it was sufficient to synthesize and use LDH powder. Meanwhile, in uses such as electrolytes in, for example, alkaline fuel cells making use of hydroxide ion conductivity, a high-density LDH membrane is desirable in order to prevent fuel gas from admixing and ensure sufficient electromotive force.
Patent Documents 1 and 2 and Non-Patent Document 1 disclose oriented LDH membranes. These oriented LDH membranes are produced by horizontally suspending the surface of a polymer substrate in a solution that contains urea and a metal salt to cause nucleation and oriented growth of LDH. The oriented LDH membranes of these Documents each show a strong peak of (003) plane in the X-ray diffraction pattern.